1. Field of the Invention
The present invention, in general relates to pumping cement and, more particularly, to a filter screen for use with a concrete pump.
It is common to pump cement at various job sites because the cement truck cannot directly access the location where the cement is to be poured. It is common to use a trailerable pump to convey the cement where desired. A trailerable pump includes an engine that drives a pump. Cement is deposited by the cement truck through a large (primary) grate into a hopper and the pump urges the cement through a hose that is routed to where the cement is needed. The trailerable pump is attached to a trailer (bed) and is towed to and from each job site as needed. This type of equipment is commonly referred to as a “trailerable cement line-pump” or more simply as a “trailerable line-pump”.
One problem involving the use of the trailerable line-pump is caused by impurities in the cement mixture. Because the mixture is not as consistent as is desirable the inconsistencies can cause a clog to occur in the hose. For example, a typical mixture of cement that is being delivered in the cement truck might be what is called “three-quarter rock and pea gravel” mix meaning the cement includes rock ranging typically from ¾ to 1 inch in diameter and/or pea gravel ranging in size from ⅜ to ½ of an inch in diameter. If the rock size is not larger than this size then there is usually no problem pumping the cement mixture through the hoses.
However, sometimes larger and even much larger rocks can be present in the mixture that can clog the hose. The primary grate that may be included with the trailerable line-pump is not able to prevent the passage of these objects because its opening size is too large, for reasons as are discussed hereinbelow that relate to flow rate. Accordingly, the primary grate that may be included is useful in preventing the passage of only the largest of objects that are several inches or more in diameter.
The typical solution to this problem at the job site is to take a sledge hammer and literally pound an obstruction (i.e., the rock causing the obstruction) that is causing a clog in the hose until the rock is crushed to a small enough size so that it can then be pumped downstream in the hose along with the rest of the cement mixture.
This process requires repeated pounding on the outside of the hose at the location of the obstruction and it is especially damaging to the hose which can cause considerable fraying on the inside of the hose. The frayed parts (i.e., cords) then tend to accumulate cement which dry in thicker and thicker layers with each subsequent usage until the cement-covered frayed cord area can itself either cause or contribute to another blockage occurring in the hose and a repetition of the pounding and further fraying of the hose until the hose is ruined.
Not only are larger than normal rocks sometimes present in the cement mixture, but all manner of objects can also be found to occur in the mixture, for example tools like pliers, sometimes find their way into the mixture. Once these are objects are deposited in the hopper of the trailerable line-pump they can damage the pump and obstruct the hose, as well. All manner of objects can cause obstructions in the hose with the same remedy as was described hereinabove.
The use of a sledgehammer to pound the hose damages the hose and this increases the frequency of hose replacement and therefore also the cost of operating a trailerable cement line pump.
The use of a simple screen placed over the hopper is ineffective for a number of reasons. The screen can collect fiber hairs, as are commonly used in cement mixtures, and clog. It is difficult to remove known types of screens to facilitate the cleaning of the fiber hairs off of them.
Also, it is difficult to select an effective screen size. The words “screen” and “grate” are used interchangeably herein. Too large of a screen size allows too large of an object to pass through which can clog the hose or damage the pump. A smaller screen size, while preferable to limit object size, fails in that it restricts the flow rate of cement into the hopper. The cement truck operators are under time pressure to deliver the cement and leave and are generally unwilling to wait in order to accommodate a slow pour rate.
A smaller screen size is also especially prone to clogging in that the objects that are retained tend to accumulate all along the surface.
Similar problems occur with truck mounted pumps and with boom pumps. Boom pumps include an extendable boom for remotely accessing a pour site over an obstruction. The instant invention is applicable for all such uses.
Another problem when pumping concrete is that sometimes the cement (concrete) is not uniformly mixed. Dry patches may exist and these are known as either “dry packs” or sometimes as “meatballs” because of their shape. Meatballs can obstruct the pumping process as much as can any sort of an obstruction present in the concrete mix. Therefore, it is important to be able to remove them as well.
Accordingly, there exists today a need for a secondary screen for a concrete pump that filters larger objects while allowing for higher flow rates.
Clearly, such an apparatus would be a useful and desirable device.
2. Description of Prior Art
Trailerable line-pumps, truck mounted concrete pumps, and boom pumps that include a hopper and a large grate are, in general, known. While the structural arrangements of the above described devices, may at first appearance, have similarities with the present invention, they differ in material respects. These differences, which will be described in more detail hereinafter, are essential for the effective use of the invention and which admit of the advantages that are not available with the prior devices.